In radioactivity measurement it is often required to determine the activity resulting from transuranic elements, namely those elements with an atomic number greater than ninety-two. It is known to use curve fitting methodology to determine transuranic activity. However, very often a transuranic activity peak will be very close to another activity peak. This poses a problem for the curve fitting methodology which cannot easily handle two peaks. We therefore seek to provide an improved method and apparatus for measuring transuranic radioactivity.